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Whatever one thinks of the “95% effectiveness” claims, even the most enthusiastic commentators have acknowledged that measuring the vaccine’s effectiveness two months after dosing says little about the duration of immunity induced by the vaccine. the vaccine. The concern, of course, was a decrease in efficiency over time. ‘Waning immunity’ is a known problem with influenza vaccines, with some studies showing almost no effectiveness after just three months, meaning that a vaccine taken early may ultimately provide no protection by the time the ‘flu season is over. flu ”comes a few months later.
If the vaccine’s effectiveness wanes over time, the crucial question becomes what level of effectiveness will the vaccine provide when a person is actually exposed to the virus? Unlike Covid vaccines, the performance of the influenza vaccine has always been judged over a full season, not a few months.
And that’s how recent reports from the Israeli Ministry of Health caught my attention. In early July, they reported that the effectiveness against infections and symptomatic illnesses “fell to 64%”. By the end of July, it had fallen to 39%, with Delta being the dominant strain. It is very weak. For context, the FDA expectation is of “at least 50%” effectiveness for any vaccine that can be approved.